Remote echo ranging system



y 8,. 1954 E. H. KRAUSE ETAL 2,679,041

REMOTE ECHO RANGING SYSTEM Filed Oct. 10, 1945 a Sheets-Sheet 1 N f fIMPULSE ANTENNA ECHO TR ANSMITTER SWITCH RECEIVER TRANSMITTER RECEIVE-RSIGNAL SWEEP SELECTOR GENERATO P v I I SIGNAL SWITCHING SELECTOR CIRCUITERNST H. KRAUSE MILTON W. ROSEN NOLAN R. BEST W W y 1954 E. H. KRAUSE ETAL 2,679,041

REMOTE ECHO RANGING SYSTEM Filed Oct. 10, 1945 8 Sheets-Sheet 2 ANTENNASWITCH 2| \i/ MODULATING FROM f OSCILLATOR RELAY RELAY AME MODULATINGOSCILLATOR g j g V ANTENNA I l I k i OSCILLATOR I L l CONTROLLED ECHOAMQRELAY CHANNEL AM P. 7 A.V.C.OUTPUT RECEIVER grvuorvbwu ERNST H.KRAUSE MILTON w. ROSEN 5w NOLAN W May 18, 1954 E. H. KRAUSE ETAL REMOTEECHO RANGING SYSTEM Filed We. 10, 1945 8 Sheets-Sheet 3 ERNST H. KRAUSEMILTON W. ROSEN NOLAN R. BEST M IIHI May 18, 1954 E. H. KRAUSE ETAL2,679,041

REMOTE ECHO RANGING SYSTEM Filed Oct. 10, 1945 8 Sheets-Sheet 4 ALLAvvvv llll vvvv

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1; 98 l 97 AVCVOIJ'AGE TO 4- FRpM 7 AAAAAA vvvvv A-AAAAA ERNST H. KRAUSEMILTON W. ROSEN NOLAN R. BEST wkw f May. 18, 1954 E. H. KRAUSE ETAL2,679,041

REMOTE ECHO RANGING SYSTEM Filed Oct. 10, 1945 8 Sheets-Sheet 5 L L L RR 0 AMA AMA AMA AMA AMA N H H H H @AMA @AMA @AMA AMA @AMA ERNST H. KRAUSE MILTON W. ROSEN 35 NOLAN RBEST May l8, 1954 H. KRAUSE ETAL 2,679,041

REMOTE ECHO RANGING SYSTEM 8 Sheets-Sheet 7 Filed 001;. 10, 1945 ERNST.H. KRAUSE MILTON w. ROSEN NOLAN R. BEST E. H. KRAUSE ETAL 2,679,041

REMOTE ECHO RANGING SYSTEM May 18, 1954 Filed Oct. 10, 1945 8Sheets-Sheet 8 INPUT 70 708E 20/ ERNST H. KRAUSE MlLTON W, ROSEN NOLANR. BEST Patented May 18, 1954 REMOTE ECHO RANGING SYSTEM Ernst H.Krause, Cheverly, Md., and Milton W. Rosen and Nolan R. Best,Washington, D. 0.

Application October 10, 1945, Serial No. 621,637

(Granted under Title 35, U. S. Code (1952),

sec. 266) 19 Claims.

This invention is directed to the problem of transmitting theinformation obtained from an echo ranging installation to a remotepoint.

In the use of echo ranging systems for obstacle detection, it isfrequently desirable that the information obtained from the echo rangingsystem should be instantly available at a remote location. Thus, acentral monitoring position may be provided for a multiplicity of echoranging installation. Under other circumstances, it may be desirable toindicate remotely the detailed obstacle distribution in the immediateneighborhood of an echo ranging installation. This is particularly truewhere a mobile high resolution echo I ranging system is employed totransmit information to a remote point, where the same information couldnot conveniently be obtained from an echo ranging installation at thatpoint. The latter situation is particularly apt to arise in connectionwith mobile unattended craft.

It is accordingly the object of the invention to provide for the remotetransmission of information obtained from an echo ranging system.

The invention will be further described with reference to the exemplaryembodiment disclosed in the drawings, in which:

Figure 1 shows in block diagram an exemplary embodiment of theinvention,

Figure 2 shows in block diagram a transmitter unit and associated keyingcircuits for transmitting the echo ranging information according to thepresent invention,

Figure 3 shows a transmitter unit and associated keying circuits inschematic diagram for transmitting the echo ranging informationaccording to the present invention,

. Figure 4 shows an automatic volume control system for the unattendedecho ranging receiver,

Figure 5 shows representative control and reception wave forms in theecho ranging installation,

Figure 6 shows in block diagram a signal separator for employment with areceiver at a remote point from the echo ranging installation,

Figure '7 shows a controlled amplifying channel in the signal separatorof Figure 6,

Figure 8 shows an indicator control circuit included in the signalseparator shown in Figure 6,

Figure 9 shows an automatic volume control system for use in theinstallation shown in Figure 6,

Figure 10 shows representative wave forms at points in the signalseparator of Figure 6.

The transmission system of the present invention is particularly adaptedfor operation with echo ranging systems employing radio impulsetransmission and echo reception. The present invention is furtheradapted for employment with radio echo ranging system which yieldinformation concerning the angular position or azimuth of an obstacle aswell as the range thereof. In the specific embodiment to be described,the radio echo ranging system gives information additionally on theposition of an obstacle with respect to which side of a referencedirection it lies. The specific radio echo ranging system illustratedand described in the exemplary embodiment is similar to that disclosedin Patent No. 2,546,170 of George C. Schleter et al., filed December '7,1942 for Radio Echo System for aircraft.

This system is diagrammatically disclosed in Figure l, and in thefollowing figures. It characteristically includes two antennas i and 2,having directive characteristics, disposed at an angle to one another.The mean direction of the antennas may be conveniently oriented with thelongitudinal axis of the craft. The antennas are successively employedin the operation of the system, and by compari on of their respectiveecho amplitudes it may be ascertained to which side of the meandirection the obstacle being ranged upon is located. The system includesa periodically operative impulse transmitter 3 whose output is connectedto the antenna system through switch 5.

It will be understood, particularly with reference to the abovementioned application, that the transmitter impulses are communicated byswitch 5 to antenna or antenna 2. The echos received on the respectiveantenna carrying the'impulse are applied to receiver i and the outputfrom this receiver is indicated on a cathode ray tube. Each antennacarries a series of transmitter impulses, following which the system isswitched to the other antenna. The echoes are indicated in differentpositions on this tube for each antenna, and the echo amplitudes may becompared on the two indications. It may therefore be ascertained whetheran obstacle is yielding a larger amplitude echo on antenna i or onantenna 2. The obstacle will yield the larger echo amplitude on theantenna with which it is more nearly aligned. By maneuvering theinstallation, or the vehicle on which it is applied, to obtain equalecho amplitudes from an obstacle, the mean direction of the antennainstallation may be oriented toward that obstacle.

In the conventional echo ranging system, the information obtainedthereon is normally locally indicated. This is also true in the systemof the application above referred to. In the present system however,this information is not necessarily locally indicated, and indicatingmeans for this purpose are not shown. The information obtained is,however, transmitted to a remote point from transmitter 6. Thistransmitter operates to relay the output of receiver i and is furthercontrolled by suitable signals obtained from impulse transmitter 3 andfrom antenna switch 5.

The detailed operation of the transmitter and its associated circuitswill be described in. connection with subsequent figures of the drawing.The link transmitter output is received on antenna ill by a remotelypositioned link receiver 7, whose output is fed through a separator 85which is selectively responsive to various signal components radiated bytransmitter 6. The'out put of separator 8 is employed for controllingand applying the information to indicator 8, which is conventionally acathode ray type of instrument.

The radio echo ranging system obtains information relative to theobstacle direction and range. This is applied as a composite signal tolink transmitter 8. The signal components are separated in the outputnetworks fed from remote receiver 1. Thus, one component is selectivelytransmitted through a selector network to operate the cathode ray tubesweep generator. Another series of components is passed to the indicatorin a manner to characterize the direction of echo ranging. The separator8 of Figure 1 is also shown to include an automatic volume controlcircuit of special construction which is effective in stabilizing theoperation of the remote indication system.

As will be understood, is necessary to transmit the amplitudes of theechoes received by receiver their time relation with respect to thetransmitter impulse, and also information relative to which antenna isoperative at the time the respective echoes are received. Consequentlythe control circuits for the transmitter 6 are responsive to asynchronizing signal coinciding with the operation of the impulsetransmitter, the radio echo signals derived from the transmitter impulseradiation, and a signal selectively characterized in dependency onwhether antenna switch 5 is causing transmission from antenna l orantenna 2.

In the system above referred to, impulse transmitter 3 is operated anumber of times during each cycle of the antenna switch 5. Thus, onsuccessive series of transmitter operations, antennas l and 2 arealternately employed. The output signal of receiver 6 under this type ofoperation is shown at line A in Figure 5, where the left and rightsignal groups correspond to those obtained from antennas l and 2respectively. The signal groups in line A correspond to the end of aleft antenna series and the beginning of a right antenna series. Theecho signals indicates three obstacles positioned along the mean antennaaxis.

As shown in Figure 2 transmitter 6 may include an oscillator l l drivinga modulated power amplifier E2. The output of the power amplifier 52 maybe radiated by any suitable antenna 62. The output of echo receiver l,which may resemble the wave form shown at A in Figure 5, is directlymodulated on the amplifier so that the time relations of the echosignals together with their amplitudes are transmitted.

In order to characterize the transmitter impulse so that this componentof the echo receiver output may be selected without confusion with ahigh amplitude echo signal, a synchronizing signal obtained directlyfrom impulse transmitter 3 is supplied at terminal 54 and is caused toadditionally modulate power amplifier l2 simultaneously with thiscomponent which is received from the echo receiver. This synchronizingsignal applied at terminal i l is shown at line B in Figure 5, andcauses the output of the power amplifier to have the wave form shown atline C in Figure 5. As may b se th ynd chronizing signal has aconsiderably greater amplitude than that possessed by the echo signals.

For the purpose of the invention, it is particularly desirable that themaximum amplitude of an echo signal delivered from receiver 4 bemaintained at a relatively constant voltage. For this purpose anautomatic volume control system is provided, shown in Figure 2. In orderthat this system may respond only to the amplitude of the received echo,and will be independent of the transmitter impulse itself as deliveredfrom receiver, it is operative only during a short period subsequent tothe transmitter operation. For this purpose a relay [6 is providedoperating in dependency on the transmitter synchronizing signal derivedat terminal i l. The relay output provides a control signal for alimited period following the operation of the transmitter. Normally thistime period will encompass the echo signal group which is received inconsequence to a transmitter impulse. The relay signal is applied to acontrolled channel H, which receives the echo signal output andtransmits the same to amplifier it during the duration of the relayoutput. Amplifier i8 feeds the AVG diode [9 whose output is employed toenergize the AVG network of echo receiver 4.

The antenna lobe identification signal is obtained in dependency onoperation of a component of the antenna switch. As shown at 2| in Figure2 this switch will include two opposed contacts and a travelling brushmember driven synchronously with the means controlling the antennaswitching. On alternate antenna operation, the opposed switch elementsare successively connected with ground as shown in the drawings. Thisantenna switch is employed to control selectively a pair of modulatingoscillators of differing frequencies which are employed to apply a lobeidentification signal to power amplifier i2. For this purposeoscillators 22 and are provided. These oscillators may be convenientlycontrolled by connecting the oscillator tube cathodes to the opposedswitch elements so that one or the other of the oscillators may begperated in accordance with the antenna selecion.

The oscillators are keyed in dependency on the impulse transmittersynchronizing signal which is delivered to terminal iii. In order thatthe lobe identification signal may be transmitted without interferencewith the echo signal output, suitable time delay means are provided. Asshown, this may constitute a pair of relays 25 and it. Time delay relay25 becomes operative in dependency on the transmitter synchronizingsignal and after a selected period keys oil relay 26. The latter relayis characterized in maintaining an output'having a time duration equalto that during which it is desired to radiate a lobe identificationsignal. The output of relay 2B is shown at line D in Figure 5. As may beseen there, relay 25 is keyed into operation a period following thetransmitter synchronizing impulse which is determined by thecharacteristic of relay 25, and that duration of the output of relay 26is suitably proportioned to effect the proper identification signal.

As shown in line E which indicates the output of the modulatingoscillator 22, the latter is keyed previously to each signal groupcorresponding to .operation of left antenna 5. Oscillator 22 isoperative during the alternate operations of antenna switch 21, independency on the operation of relay 26. As will also be seen from lineF,

Figure 5, operation of modulating oscillator'23, which characterizes theimpulse signals derived from operation on right antenna 2, takes placeduring the succeeding period. It will be understood that the modulatihgoscillators 22 and 23 are designed to oscillate at difierent frequencieswhich are selectively responded to in the receiving system forsynchronizing the desired sweep presentation. The output of theoscillators is applied through amplifier 2'! to power amplifier i2,which is accordingly caused to radiate at antenna I3 the desiredmodulated lobe identifying signal.

The signal radiated by power amplifier l2 under the various signalsintroduced thereto is shown in line G in Figure 5. This signal comprisesthe Figure 3 shows in schematic diagram the power amplifier l2 togetherwith modulating oscillators 22 and 23 and their control relays 25 and26. In this embodiment shown the power amplifier comprises pentode tubes3i and 32, which are. .driven in push-pull relationship from oscillatorII. The amplifier may be amplitude modulated from the center tap of thegrid tank coil 33. The plate tank circuit output is coupled inductivelyto coil 34 which is connected to a suitable transmission line forfeeding antenna iii. The output of echo receiver 4 is supplied atterminal 35 as a positive voltage signal group and coupled to theamplifier for grid amplitude modulation through coupling condenser 36.

The transmitter synchronizing signal which is delivered directly toterminal 14 is coupled into the amplifier for simultaneous plate andscreen grid modulation. Thus the signals introduced at terminals 35 andI4 establish operation of the amplifier to generate the signal shown atline C of Figure 5. The operatin conditions of the power ampli- 'fierincluding tubes 3| and 32 is such that normally a low CW output ismaintained on the frequency of oscillator I l. The grid modulatingsignals effect substantially linear class A modulation, so that the echoamplitudes are modulated on the amplifier output in accordance withtheir relative strength. The simultaneous control grid, screen grid, andanode modulations effected in synchronism with the operation of theimpulse transmitter drive the power amplifier to substantially twice themodulation amplitude which is effected by the lobe identificationsignals and maximum echo signals.

As pointed out above the lobe identification oscillator 22 and 23 arekeyed into operation by relay 26, whose operation is instituted by timedelay relay 25. The oscillators comprise tubes M and 42 respectively asshown in Figure 3. Keying relay 26 includes tubes 53 and t l, and timedelay relay 25 includes tubes 45 and 45. The latter are conventionalKipp relays, having one stabl condition, and being thrown over into theother condition by the injection of a synchroniz- It is also preferablefor use with the ing signal. The period of operation is determined bythe RC time constant in the grid circuit of the tube conducting instand-by.

In the time delay relay, grid 4'! of tube is returned through variableresistance 43 to a positive source of potential 49. Grid 50 of tube 45is returned to a source of negative potential 5| by which its voltage ismaintained below that of cathode 52 of tube 45. Consequently in relaxedcondition this relay conducts in tube 45, Whereas tube 45 is normallyblocked. The potential at anode 55 of tube 45 is therefore well belowthat of the positive potential source 49, whereas anode 56 is normallyat supply potential. The transmitter synchronizing impulse which isdelivered to terminal !4 has a positive polarity and is introduced togrid 50 of tube 46 through condenser 58.

Upon operation of the impulse transmitter, tube 35 is therefore keyedinto conduction and tube 55 is blocked. This condition is maintainedduring the interval determined by the time constant of the grid of tubet5, which is the product of the capacity 55 and the resistances in thegrid circuit resistors 48 and 58. As shown in Figure 5 this interval iseffective to produce the delay between the pip shown in line B whichcorresponds to the transmitter synchronizing impulses and the leadingedge of the square wave signals shown in line D. Upon relaxation of thisrelay a negative voltage appears at anode 55 of tube 45, which iscommunicated through capacity iii to grid 62 of tube i3.

Tubes 53 and 14 constitute the lobe identification synchronizing keyingrelay and are connected similarly to tubes it and 36. Grid 52 of tube 43is returned to the positive potential source as grid or tube id isreturned through series resistor 54 to a source of negative potential5!. Consequently tube 63 is normally conduct ng and tube is is normallynon-conducting. Anode 55 of tube 43 maintains a low potential exceptwhen this tube is blocked.

l3locking of tube s3 is effected by the negative voltage applied to itsgrid upon relaxation of the time delay relay. The blocking period isdetermined by the time constant on grid 52 of tube 53. During thisinterval anode5 of tube 53 is maintained positive and tube it is held inconduction through the resulting voltage applied to grid 53. It will benoted that the latter positive voltage shift is also appliedsimultaneously to grid 5! of tube 42 and grid 68 of tube ii.Consequently, tubes ii and G2 are thereby thrown into a con dition forconduction during conduction of tube M.

The connection of grids El and 55 with grid 53 of tube t4 puts theantenna lobing identification tubes 4i and 62 under coordinate controlwith tube of the keying relay. Consequently, the lobe identificationoscillators may only be operated during the operative period of thekeying relay.

As shown in Figure 3, the lobe identification oscillators comprise tankcircuits El and 72 connected with the grid and cathode of tubes 4! andQ2. The cathodes are returned to ground through switch 2! which isoperated synchronously with the antenna switching means 5 of the rangingsystem. Consequently, under the control of the keying voltage from thekeying relay and under control of antenna switch 2 i, tube 4: willsupply the output shown at line F in Figure 5, and tube l2 will thensupply the output shown at line E of Figure 5. The outputs of tubes iiand 42 are obtained from their anode circuits, which. are connected inparallel. This signal is, applied through capacitor it to ampliiyingtube The outputv of this tube is coupled through condenser 16 to thecenter tap of grid coil 33 of the power amplifier. The oscillatorcircuits of tubes M and 42 are adjusted to eifect equal amplit debetween the two oscillators. It will therefore be seen that suitablemodulating signals are applied to the power amplifier to effect amodulation envelope as shown in line C- of Figure 5.

The automatic volume control system for the radio echo receiver which isshown in block diagram in Figure 2 will be further described withreference to Figure 4. This circuit includes a relay having tubes 3! and82, which is on responsively to the impulse transmitter synch. nizingsignal delivered at terminal i l. Grid 33 of tube SI is returned to thepositive potential source are and grid 34 of tube 82 is maintained at anormally low potential by its return to negative potential source iii.Consequently, tube SI is normally conducting and tube 32 is normallyblocked. The relay is thrown over response to the positive synchronizingsignal introduced on grid 84 of tube 82. The time constant of the gridcircuit of tube Si is selected to efiect relaxation of the relay afterthe receipt of the desired echo signal. During the operation or therelay a positive voltage is present on the anode of tube M, which is fedto grid 85 of control tube 88 through condenser 8?. Tube comprises thecontrolled channel for the AVG circuit. This tube is normally blockedthrough the return of grid 35 to the negative potential source 55, andis non-conductive except during the limited operating period of thecontrol relay. The echo receiver output is applied to the anode of tubeat terminal 88, whereby the tube operates as a diode responsive to thereceiver output. The positive echo signals develop a negative voltageacross capacitor as in accordance with their amplitude, and this voltageis applied to control grid 95? of tube 9|.

The A. V. C. diode output circuit is responsive to the maximum echosignal amplitude due to the long time constant of resistance Itfl andcondenser 89. Tube 8! is a direct coupled amplifier which may be set tothe desired operating condition by cathode voltage divider $2.

The average potential of grid 90 of tube 9i will therefore be maintainedin accordance with the maximum amplitude of the echo signals received onthe echo receiver. The anode 3 of this tube is direct coupled to grid 95of tube 98. 97 of the automatic volume control output tube 96 thereforesupplies at terminal as an automatic volume control for reintroductionto the suitable intermediate amplifier grids of the radio echo receiver4.

The A. V. C. components described, it will be understood, are desira leon unattended installations to prevent saturation in systems wheredirectional indications are obtained through echo signal amplitudecomparison.

Through the operation of this automatic volume control system, theoutput of echo receiver 4 is maintained so as to effect substantiallyconstant maximum amplitude modulation of the power amplifier I2.Consequently, the receiver and indicator of the remote installation willbe supplied with a stable signal.

Link receiver 1 shown in Figure 1 may be conventional and is thereforenot shown in detailed circuit diagram. It may include a preliminary Theanode left indicator channel terminal II5.

' chronizing impulse.

radio, frequency amplifier stage, a converter, and a plurality ofintermediate amplifier stages. The control grid of the amplifier stagesmay be returned to an automatic volume control connection which will besupplied with a suitable voltage by means to be described below. Theintermediate amplifier output may be rectified, further amplified, andthen connected to terminal IIII, as shown in Figure 6.

In this figure is shown in block diagram the operating components andthe operative connections between the same of the separator unit I shownin Figure 1. This unit functions to separate the alternate series ofsignal groups in accordance with the lobe identification signal, and tosupply the transmitter and echo signals in two separate channels. Theseparator also includes components responsive to the transmittersynchronizing impulse which is of higher amplitude than the othersignals of the signal group. Also shown in Figure 6 is an automaticvolume control circuit for receiver i.

The detected output of receiver i, which is supplied at terminal IilI,is coupled to grid I02 of tube IE3 through capacity Ill-i. Tube I03 isconnected as a cathode follower whose output is supplied to bus I85through radio frequency choke coil I06 and capacity I07.

The receiver output signal which is present at bus I is delivered toamplifier IID which feeds two controlled channels III and H2. The outputof channel III is fed to amplifier II3 which is coupled through cathodefollower II to the Channel II2 feeds amplifier H6 which is coupled tooutput channel II'I through cathode follower IIB. Transmission ofchannels III and H2 is selectively controlled in dependency on the lobeidentification signals.

For this purpose the receiver output is fed through amplifiers I2I andI22 to a pair of tuned detectors I23 and I24. These detectors areselectively responsive to the lobe identifications signal frequencies.The two detector outputs are fed through base clippers I25 and I26 forthe purpose of removing low level noise. The detector outputs areeffective at the end of the lobe identification signals to throw intooperation relay I21 or I28. The relay outputs are effective to permittransmission through the controlled channels during a sufiicient timeperiod to accommodate the transmitter synchronizing impulse and thereceived echoes.

By the operation of the above circuit, the successive echo signals arefed through the alternate indication channels. The indicator sweepcircuit, however, is required to respond to each of the signal groups.For this purpose the output of relays I21 and I28 are both fed to mixerI30. The output of this mixer is operative at the end of each lobeidentification signal to key into operation relay 13!. .,e1ay I3I isprovided with a limited operating period which is sufficient toencompass the receipt of the transmitter syn- This impulse signal ispresented to controlled channel I32 by amplifier I33 fed from thereceiver bus Hi5. Channel I32 is over-biased to an extent sufficient toreject all signals except the synchronizing impulse which, as describedabove may be of substantially twice the echo and lobe identificationsignal amplitude. Controlled channel I32 is maintained biased so as tobe totally inoperative exceptin response to operation of relay I3I.Consequently, the output of controlled channel I22 9 consists of asingle impulse appearing at the pulse repetition frequency of the radioecho ranging system, and this is fed to amplifier lit, which is coupledto the synchronizing signal channel I through a cathode follower stageI38.

The automatic volume control system for receiver I is responsive only tothe lobe identification signal amplitudes. As described in connectionwith the transmitting system, this is substantially equal to the maximumamplitude of a received signal pulse. The AVC system includes mixer Iwhich is responsive to the output of both tuned detectors I23 and 22s.I40 feeds an amplifier I lI which operates on a controlled channel M2 topermit the passage of the lobe identification signal from the receivingset. The lobe identification signal is fed through the amplifier I43 toan automatic volume control diode of a conventional type I44. The diodeoutputis connected directly to bus IE5 which is therefore supplied withdirect current potential providing the receiver automatic volume controlvoltage. This voltage is filtered through series resistor I45 andcondenser IE6 to supply the desired potential of terminal It! for con-1.

nection to the receiver automatic control bus.

The lobe identification signal controlled transmission channels, whichfeed the indicator units, are identical to each other, with theexception of the resonant frequency of the tuned detectors I23 and I24.For this reason only one channel will be described in detail, and thisis shown in an exemplary embodiment of Figure '7 in the drawings.

The receiver output signal may be introduced at terminal I5l in Figure7. The signal is fed through amplifying tube I52. This amplifier iscoupled through a tuned transformer IE?- to control grid I54 of tubeI55. Tube I55 constitutes a detector which is responsive only to theappropriate lobe identification signal frequency. In order todiscriminate against interference and transient noise levels the platecircuit of tube I55 is provided with series resistor I55 and shuntcondenser I5'I. These components are selected to have a long timeconstant, which is substantially equal to the duration of the lobeidentification signal. Consequently, as the lobe identification signalmay be made to last several hundred microseconds, the anode circuit ofthis tube will be relatively unresponsive to short noise impulses.

In order further to discriminate against'low level noise the outputcircuit of tube I55 is provided with a base clipping diode I50. DiodeIttl functions as a base clipper for removing low level signals andnoise. The tube is normally conductive, and is in series with resistorI58 in the output circuit of tube I55. When the output value rises abovea limiting value, cathode IEI assumes a potential above anode I62 and asthe diode is then non-conducting, the'higher level signals are appliedto control grid Its of tube I6 5.

The operation of the circuit described will be further clarified withreference to Figure 10 which shows representative wave forms presenttherein. As in Figure 5, the end of a left lobe series and the beginningof a right lobe series of signals is shown. At A the receiver outputsignal appears which is presented to the grid of tube I52. At B is shownthe output wave form on the anode of tube I55. It will be noted that theanode of this tube is responding only to the left series of echo signalgroups which correspond to the particular lobe identification signals towhich this detector stage is resonant. At C is shown the signal afterclipping by diode I50, the low level noise variation being substantiallyeliminated therefrom.

This clipped signal is differentiated across resistor I55 in the gridcircuit of tube Nit through condenser Iiiil. This furnishes a sharpnegative voltage pip at the end of the lobe identification signal.

Tubes 56d and Iii: are coupled in a relay circuit in which tube I54 ismaintained normally conducting through the return of its control grid toa positive potential. The control grid I?! of tube I'III is returned toa negative potential I12 so that this is normally cut off. The sharppulse delivered at grid I53 of tube I5 3 on t..:mination of the waveform at C of Figure 10 blocks tube ltd to throw tube I10 into conductionby the positive voltage thereby ap-- plied to grid ill of this tube.

Grid I75 or" tube I75 is controlled simultaneously with grid ill of tubeaw. Tube H6 is thus maintained in conduction during the conductingperiod of tube I'IIJ, which period is determined by the time constant ofthe grid circuit of tube I5 3. This interval is selected to encompassthe transmitter synchronizing impulse and the received echo signalgroup.

Tube IIIB is :fed the receiver output from amplifier tube Ill. Theoutput of tube I15 is fur-. ther amplified in tube I18 and coupled tooutput channel I36 through cathode follower tube I79. Channel Iii l willbe connected with one of the deflection input circuits of cathode rayindicator 9 shown in Figure l.

In Figure 3 the circuit disclosed selects the high amplitude transmittersynchronizing signal which is required for triggering the receiver sweepcircuit.

This circuit comprises a pair of mixer tubes 35 and IBIS arranged with acommonanode resister I531. Control grids I83 and I89 are fedrespectively from terminals I98 and I9! and may be directly energizedfrom relays I2! and I28 which are shown in Figure 6. Specifically, theseterminals be connected to grid I'll of tube I'III shown in Figure 7 andto the corresponding element in the other channel, so that one or theother mixer tube is conductive following each lobe identificationsignal. This produces a resultant negative voltage swing across resistorIB'I.

The negative anode swing of tubes I and I35 is employed to control relayI3! which comprises tubes I and I95. In the circuit shown, tube I95 isbiased so as to be normally conducting and tube I95 is biased to benormally blocked. The negative voltage supplied at the output of themixer on the termination of each lobe identification signal is coupledto the control grid IQ! of tube I95 through capacity I98 to block thistube substantially'during the time constant of the grid circuit. Thiscauses a positive swing on anode I99 in tube I95 to drive tube I96 intoconduction and simultaneously open a controlled channel including tube2M.

In order to supply the receiver output to tube 29!, the receiver may beconnected to terminal 2S2 for introducing the signal to amplifying tube263. The receiver output is therefore applied to control grid 2% of tubeEilI along with the positive output from tube I99 which follows thetermination of the lobe identification signal. Cathode 205 of tube ZIIIis biased positive on voltage ure 7.

divider 298 to maintain tube 2M non-conducting except on the highamplitude transmitter synchronizing signal. Consequently, anode 201 oftube 20! is maintained substantially at positive supply potential exceptduring this synchronizing impulse. The resulting negative swing on anode291 is inverted in amplifier tube 298 and is coupled to output terminalH35 through cathode follower 2 it. The positive pulse on terminal 535 isemployed for tripping the sweep generator in the indicator unit.

In Figure 10 line D is shown the signal applied to control grid 2% oftube 20!, which is a combination of the receiver output signal and thegating control voltage from the relay I35. On line E of Figure 10 isshown the amplified output from tube 2M from which all the signal hasbeen eliminated except the synchronizing impulses which trigger thesweep circuit.

The automatic volume control system for receiver l is shown in Figure 9,and is responsive only to the lobe identification signals. The circuitcomprises a pair of tubes 2E5 and 2E6 which are provided with a commonanode resistor 2H. These tubes are provided with a positive cathode biasto clip low level noise. The control grids of the mixer tubes may beconnected at terminal 2I8 and 259 directly to the anodes of the detectors. Thus, terminal 258 in Figure 9 may be directly connected to theanode of tube I55 in Fig- The detector anode signal being a positivevoltage, anodes of tube 255 and 2&6 swingnegative during the lobeidentification signals, and this signal is applied to grid 220 of tube22! This permits anode 222 of tube 225 to swing positive durin the lobeidentification signal. This positive swing is communicated to grid 223of tube 224 which is normally biased below a conducting level by thegrid return to a source of negative voltage at terminal 225.

The receiver output voltage is applied at terminal 226 and is coupled tocathode 228 through condenser 22?. Cathode 228 is returned to groundthrough a relatively high impedance 2Z9. Tube acts as a diode detectorduring the lobe identification signals while the blockin potential isremoved from grid 223.

The detected output voltage is filtered to remove the lobeidentification modulating frequency components by condenser 235, andthen amplified and inverted in tube 2.30. In the figure, the diode isconstituted by a tube in which the grid and plate are electricallyconnected together form a unipotential conductive suriace acting as theanode in respect to the cathode. The positive output signal therefrom isapplied to an .AVC diode 233. The latter tube effects delayed automaticvolume control through the positive bias applied to its cathode which isreturned to voltage divider 233. The negative-output of the AVG networkis applied to terminal 226 and bus ['05 of Figure 6 through R.-C. filter23.3. The time constant of resistor M and condenser I46 shown in thelatter figure is suflicient to average over the lobe shifting cycle sothat the relative pulse echo amplitudes of the respective directionalindications Will be maintained.

It will be understood that the embodiment .described is exemplary of theinvention, the scope whereof is to be ascertained by reference to theappended claims.

The invention described herein may be manufactured and used by or forthe government .of

the United States of America for governmental I2 purposes without thepayment of any royalties thereon or therefor.

What is claimed is:

1. In combination, an echo rangingsystem having an impulse transmitterand an echo receiver, a radio transmitter comprising vacuum tube meanshaving control and anode electrode means, means operative to apply thereceiver output to the control electrode means, and means operative toapply a power impulse to the anode electrode means during impulsetransmitter operation.

2. In combination, an echo ranging system including a recurrent impulsegenerator, means for transmitting the impulses in different directions,and an echo receiver; a signal transmission circuit responsive to thereceiver output, and modulation control .means for the signal circuitoperative in dependency on the echo rangin system to transmit asynchronized impulse signal characterizing each direction of impulsetransmission.

3. In combination, an echo ranging system including a recurrent impulsegenerator, means for transmitting the impulses in differentdirections,and an echo receiver; a unipolar signal transmission circuit respcnsiveto the receiver output, and modulation control means for the signalcircuit operative in dependency on the echo ranging system to transmit afrequency signal characterizing the direction of impulse transmission.

4. In combination, an echo ranging system including a recurrent impulsegenerator, means for transmitting the impulses in different directions,and an echo receiver; a unipolar signal transmission circuit responsiveto the receiver output, and modulation control means for the signalcircuit operative in dependency on the impulse transmitting means totransmit a synchronized signal characterizing the direction of impulsetransmission.

5. In combination, an echo ranging system having a recurrent impulsegenerator, means for transmitting the impulses in either of twodirections, and an echo receiver; a unipolar signal transmission circuitresponsive to the receiver output, and modulation control means for thesignal circuit operative in dependency on the echo ranging system totransmit a synchronized signal characterizing the direction .of impulsetransmission.

6. .In combination, an echo ranging system having a recurrent impulsegenerator, means for transmitting the impulses in either of twodirections, and an echo receiver; a unipolar signal transmission circuitresponsive to the receiver output, and modulation control means .for thesignal circuit operative in dependency on the echo ranging system totransmit a frequency signal characterizing the direction of impulsetransmission.

'7. .In combination, an echo rangin system having a recurrent impulsegenerator, means for transmitting the impulses in either of twodirections, and an echo receiver; a unipolar signal transmission circuitresponsive to the receiver output, and modulation control means for thesignal circuit operative in dependency on the impulse transmitting meansto transmit a signal characterizing the direction of impulsetransmission.

8. In combination, an echo ranging system having. an impulse generatorrecurrently operative at a repetitionfrequency, means for transmittingthe impulses in different directions, and

an echo receiver; a signal transmission circuit responsive to thereceiver output, and modulation control means for the signal circuitoperative in dependency on the echo ranging system to transmit a signalunipolar therewith characterizing the impulse transmission directionpreceding impulse generator operation.

9. In combination, an echo ranging system having an impulse generatorrecurrently operative at a repetition frequency, means for transmittingthe impulses in different directions, and an echo receiver; a signaltransmission circuit responsive to the receiver output, and modulationcontrol means for the signal circuit operative in dependency on the echoranging system totrans mit a frequency signal unipolar therewithcharacterizing the impulse transmission direction preceding impulsegenerator operation.

10. In combination, an echo ranging system having a recurrent impulsegenerator, means for transmitting the impulses in different directions,and an echo receiver; a radio transmitter responsive to the receiver,and unipolar modulation control means for the radio transmitteroperative in dependency on the echo ranging system to transmit asynchronized signal characterizing the direction of impulsetransmission.

11. In combination, an echo ranging system having a recurrent impulsegenerator, means for transmitting the impulses in difierent directions,and an echo receiver; a radio transmitter responsive to the receiver,and unipolar modulation control means for the radio transmitteroperative in dependency on the echo ranging system to transmit afrequency signal characterizing the direction of impulse transmission.

12. In combination, an echo ranging system having a recurrent impulsegenerator, means for transmitting the impulses in either of twodirections, and an echo receiver; a pulse radio transmitter, twooscillators of different frequency, and means for causing theoscillators to modulate the radio transmitter selectively in accordancewith the direction of impulse transmission.

13. In combination, an echo ranging system having a recurrent impulsegenerator, an echo receiver, and a pair of directive impulse radiators;a unipolar radio pulse transmitter, responsive to the echo receiveroutput, a pair of modulating oscillators, and switching meansrecurrently operative to connect the impulse generator selectively toone and then to the other radiator, and to modulate the radiotransmitter accordingly selectively with one and then the othermodulating oscillator.

14. In combination, an echo ranging system having a recurrent impulsegenerator, an echo receiver, and a pair of directional impulseradiators; a unipolar radio pulse generator responsive to the echoreceiver output, a pair of modulating oscillators, switching meansrecurrently operative to connect the impulse generator selectively toone and then to the other radiator and to permit operation of one andthen of the other modulating oscillator, and means responsive to impulsegenerator operation becoming operative after a time delay period to keythe modulating oscillator selected by the switching means to modulatethe radio transmitter.

15. In combination, an echo ranging system having a recurrent impulsegenerator, an echo receiver, and a pair of directional impulseradiators; a unipolar radio pulse transmitter responsive to the echoreceiver output, a pair of modulating oscillators, switching meansrecurrently operative to connect the impulse generator selectively toone and then to the other radiator and to permit operation of one andthen of the other modulating oscillators, keying means operative tocause oscillation of the modulating oscillators during a predeterminedtime period, and time delay means becoming operative responsively to theoperation of the impulse generator after a timing period to instituteoperation of the keying means.

16. A receiver for a recurrent signal comprising an identifyingcomponent and a subsequent signal group, having a plurality of normallynonconducting receiver output channels,.and means selectively responsiveto the identifying component to render only one of said output channelsconductive during a predetermined time period for delivery of thesubsequent signal group.

1'7. In combination, a receiver for a cyclically recurring signal eachcycle of which comprises an identifying component of characteristicfrequency, a high amplitude impulse, and a succeeding signal group; acathode ray tube, and operating means for the cathode ray tuberesponsive to the receiver output to indicate the succeeding signalgroup along a timing locus inaugurated responsively to the highamplitude impulse in a position determined in dependency on thefrequency of the identifying signal.

18. In combination, a receiver for a recurrent signal comprising anidentifying component, a synchronizing impulse, and a signal group; acathode ray tube sweep generating means for said tube operative toestablish a timing locus there on in dependency on the receiver outputsynchronizing impulse, and control means for said tube selectivelyresponsive to the identifying component to indicate the signal groupcharacteristically in accordance therewith on the timing locus.

19. In combination, an echo ranging system operative to sound in aplurality of directions, a signal transmitter, transmitter control meanstherefore responsive to the echo ranging system operation to transmit asynchronized signal identifying the direction of sounding and signalscorresponding to echoes received, a remote receiver responsive to thesignal transmitter signals, indicator means fed by the receiver, andoperating means for the indicator operative responsively to the receiverto represent the echo sginals in a position determined responsively tothe direction identification signal.

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